1. Field of the Disclosure
The present disclosure relates to patterning of organic, electronic and organic electronic devices. The disclosed methods and materials are particularly useful for patterning OLED devices.
2. Discussion of Related Art
Organic electronic devices may offer significant performance and price advantages relative to conventional inorganic-based devices. As such, there has been much commercial interest in the use of organic materials in electronic device fabrication. For example, displays based on organic light-emitting diode (OLED) technology have recently gained popularity and offer numerous advantages over many other display technologies, Although solution-deposited OLED materials have been developed, the highest-performing OLED devices typically use vapor-deposited thin films of active organic materials.
A key challenge for full-color OLED displays is patterning the array of red, green and blue pixels. For vapor-deposited OLEDs, a fine metal mask having openings corresponding to the fineness of the desired pattern is conventionally used. However, a vapor deposited film builds up on the mask which may eventually narrow the mask openings or cause deforming stresses on the mask. Therefore, it is necessary to clean the mask after a certain number of uses, which is disadvantageous from the viewpoint of manufacturing costs. In addition, when a fine metal mask is increased in size to accommodate larger substrates, the positional accuracy of the mask openings becomes much more difficult, both from the standpoint of initial alignment and then maintaining the alignment during deposition due to thermal expansion issues. Positional accuracy may be improved to a degree by enhancing the stiffness of a flame of the mask, but this increase the weight of the mask itself causes other handling difficulties. Thus, a need exists for cost-effective patterning of organic electronic devices such as OLED devices, and particularly those having pattern dimensions of less than about 100 μm.
In addition to the challenges of patterning organic devices, so-called lift-off photolithography methods are used in specialized fields, but not widely accepted in industry, even for devices that utilize less sensitive materials. Lift-off resists (“LOR”) are commercially available, for example, bilayer structures based on polydimethylglutarimide (PMGI) with conventional photoresists, but have some disadvantages. To control undercut, the PMGI must be soft-baked under careful conditions, typically in a range of 150 to 200° C. Some substrates include materials that are not compatible with such temperatures. The lift-off agent for PMGI typically requires flammable solvents such as cyclopentanone which need to be heated. Even heated, the dissolution rate is slow, e.g., just 38 nm/sec at 40° C. Thus, even higher temperatures are recommended, e.g., 60° C. which is not ideal from a safety standpoint. Further, the recommended lift-off time is 30 minutes even at 60° C., which is not cost effective in many manufacturing settings. Sonication at high temperatures is therefore recommended to reduce time, but sonication may not be compatible with sensitive device architectures. Thus, there continues to be a need for improved lift-off materials and methods that are more manufacturable and less hazardous.